1. Field of the Invention
The present invention relates generally to an actively controlled suspension system for an automotive vehicle. More specifically, the invention relates to an anti-rolling suspension control system which can maintain satisfactorily high driving stability and prevent the vehicles gravity center from being lifted up even during cornering to cause substantially great lateral acceleration.
2. Description of the Background Art
The U.S. Pat. No. 4,702,490, issued on Oct. 27, 1987, to Hirotsugu YAMAGUCHI et al., and assigned to the common assignee to the present invention, discloses an actively or positively controlled automotive suspension system which includes hydraulic cylinders for generating variable damping force against relative motion of a vehicular suspension member and a vehicle body in bounding and rebounding directions for adjusting suspension characteristics and adjusting vehicle body attitude.
A similar type of actively controlled suspension systems has been disclosed in the co-pending U.S. patent application Ser. No. 060,911, filed on June 12, 1987 and assigned to the common assignee to the present invention now U.S. Pat. No. 4,801,155. Further, European Patent First Publications Nos. 02 49 246 and 02 49 209 respectively corresponding to co-pending U.S. patent applications Ser. Nos. 061,368 (filed on June 15, 1987) and 059,888, filed on June 9, 1987, both of which have been assigned to the common assignee to the present invention. The later-mentioned three inventions include features of anti-rolling and/or anti-pitching suspension control for adjusting damping characteristics at respective vehicular wheels for suppressing vehicular rolling motion.
In such prior proposed active suspension control systems damping characteristics of the suspension oriented outside of the corner, which suspension system will be hereafter simply referred to as "outside suspension systems", are harder in order to prevent outward shifting of a vehicular body gravity center due to centrifugal forces exerted on the vehicular body, and, on the other hand, damping characteristics of the suspension systems oriented inside of the corner, which will be hereafter simply referred to as "inside suspension systems" are softened for preventing damping characteristics from serving as a source of self-induced rolling motion. In the practical suspension control, suspension control the signal for the outside suspension system is increased according to an increasing of the lateral acceleration exerted on the vehicular body, which suspension control signal will be hereafter referred to as "outside suspension control signal", and, on the other hand, the suspension control system for the inside suspension system, which is produced by inverting the outside suspension control signal, is decreased inversely proportional to the increasing rate of the outside suspension control signal, which suspension control system for the inside suspension system will be hereafter referred to as "inside suspension control signal." By such strategy of suspension control, minimum fluid pressure to be generated in a working chamber of the inside suspension system is set to be reached at a predetermined lateral acceleration. On the other hand, the fluid pressure in the working chamber of the outside suspension system does not reach a predetermined maximum pressure at the predetermined lateral acceleration. Therefore, when the lateral acceleration exerted on the vehicular body becomes greater than the predetermined lateral acceleration, the fluid pressure of the working chamber in the inside suspension system is maintained at a minimum pressure and only the fluid pressure of the working chamber of the outside suspension system is increased toward a predetermined maximum pressure. When the lateral acceleration becomes substantial, increased fluid pressure in the outside suspension system becomes a source of vehicular attitude change to cause lifting of the outside of the vehicular body leading lifting up of the gravity center. This gives a feeling for the passenger in the vehicle that the vehicle is shifting upward toward the outside, to cause degradation of the riding comfort.